Circuit board for peripheral circuits of high-capacity modules, and a high-capacity module including a peripheral circuit using the circuit board

ABSTRACT

The present invention has an objective to provide a circuit board for a peripheral circuit which can transmit outside heat which generates from a high exothermic element, such as a power semiconductor element, while attaining reduction in size and weight, reduction in surge, and reduction in a loss, in high-capacity modules including power modules, such as an inverter. 
     [Solution Means] In a high-capacity module, by laminating a peripheral circuit using a ceramic circuit board with electrode(s) constituted by thick conductor and embedded therein on a highly exothermic element, overheating of the module is prevented by effective heat dissipation via the circuit board while attaining reduction in size and weight, reduction in surge, and reduction in a loss in the module.

BACKGROUND OF ME INVENTION

1. Field of the Invention

The present invention relates to a circuit board for peripheral circuitsof high-capacity modules. More particularly, the present inventionrelates to a circuit board for peripheral circuits to be laminated witha circuit containing a high exothermic element in high-capacity modulesincluding power modules, such as an inverter used in a hybrid car or anelectric vehicle, etc. Furthermore, the present invention also relatesto a high-capacity module including a peripheral circuit which uses thecircuit board.

2. Description of Related Art

Conventionally, in high-capacity (large electric power) modulesincluding power modules, such as an inverter, a circuit containing apower semiconductor element, such as a switching element (for example,IGBT (Insulated Gate Bipolar Transistor)) (may be referred to as a“power circuit” henceforth) and a peripheral circuit which controls sucha power semiconductor element (may be referred to as a “drive circuit”henceforth) are arranged planarly, and the area for arranging the wiring(wire) for connecting these circuits is required, and these have becomea factor for preventing reduction in size and weight of a high-capacitymodule (for example, refer to FIG. 2).

In the present specification, a high-capacity module refers to a modulehandling a large electric power with a voltage of 200V or more or acurrent of 10 A or more. As a specific example of such a high-capacitymodule, for example, what is called a “power module” etc. can beexemplified.

Moreover, concerns that wiring length becomes longer due to the wiringfor connecting various circuits which constitute high-capacity modulesas mentioned above, the loss as the whole module becomes larger, and thesurge voltage which generates on switching due to the equivalentinductance of the wire becomes larger have been recognized. Excessivesurge voltage has a possibility of damaging, for example, asemiconductor element in a drive circuit, etc.

By the way, in recent years, for example, along with the popularizationof hybrid vehicles and of electric vehicles etc., further improvement inperformance such as reduction in size and weight, reduction in surge(surge control), and higher-efficiency (reduction in a loss), etc. hasbeen increasingly demanded.

Then, approaches to laminate circuit boards for various circuits whichconstitute high-capacity modules as mentioned above in order to attainreduction in size and weight of the high-capacity modules and to improvethe connection configuration between the various circuit boards whichconstitute the high-capacity modules in order to attain reduction insurge and reduction in a loss have been proposed (for example, refer toPatent documents 1 to 3).

However, when various circuit boards which constitute a high-capacitymodule are laminated as mentioned above, reduction in size and weight ofthe module can be attained, while it may become more difficult totransmit and release heat which generates from a power semiconductorelement, such as a switching element and, therefore, there is apossibility that a problem, such as breakage of the module (for example,degradation of sealing resin of a circuit element which constitutes themodule) etc. may occur.

In the present specification, a high exothermic element refers to anelement whose temperature may reach 120° C. or higher in its operatingstate. As a specific example of such a high exothermic element, forexample, a power semiconductor element etc. can be exemplified.Moreover, as a specific example of such a power semiconductor element,for example, a switching element etc. can be exemplified. Furthermore,as a specific example of such a switching element, for example, an IGBTas mentioned above, an SiC-MOSFET which will be mentioned later, etc.can be exemplified.

To problems as mentioned above, an approach to stick a leadframe to anundersurface of a circuit board of a drive circuit laminated on a powercircuit containing a switching element and thereby release heatgenerated from the switching element in a direction toward an uppersurface (upper direction) of a module through the leadframe whilereducing a switching loss and switching surge has been also proposed(for example, refer to Patent Literature 1 (PTL 1)). However, in such aconfiguration, since the pathway to the upper direction of the heatgenerating from the switching element is limited to the leadframe, thereis a possibility that the heat dissipation effect may becomeinsufficient.

Moreover, when a resin circuit board is used in a drive circuitlaminated with a power circuit, there is a possibility that, due to heatgeneration from the power circuit, the resin circuit board may expandand/or deform and it may lead to decrease in reliability and/or lead todisconnection or destruction of the circuit at worst.

On the other hand, as a loss remedy of a power semiconductor elementincluding IGBT, MOSFET, etc., it has been proposed to use a siliconcarbide (SiC) wafer in place of a silicon (Si) wafer which has been usedconventionally. This SiC wafer has a feature that an operation at highertemperature is possible, as compared with a conventional Si wafer.Thereby, a cooling mechanism (for example, a heat sink, a water-coolingmechanism, etc.) which has been indispensable in a power module whichuses a conventional Si wafer can be drastically simplified. As a result,reduction in size and weight of a power module can be also attained byusing a SiC wafer. However, there is a tendency that various problemsdue to heat generation from a high exothermic element as mentioned abovebecome still severer by a rise of an operation temperature of the powermodule accompanying use of a SiC wafer.

Moreover, since thickness of a conductor used in a peripheral circuit isthin, there is also a subject that the loss at the time of passingcurrent is large.

CITATION LIST Patent Literature

-   [PTL 1] Japanese Patent Application Laid-Open (kokai) No.    2006-303006-   [PTL 2] Japanese Patent No. 3410696-   [PTL 3] Japanese Patent Application Laid-Open (kokai) No. 2011-23654

SUMMARY OF THE INVENTION Technical Problem

As mentioned above, along with progress of reduction in size and weightand a rise of an operation temperature in high-capacity modulesincluding power modules, such as an inverter, problems, such as breakageof the module etc. (for example, degradation of sealing resin of acircuit element which constitutes the module, expansion and deformationof a resin circuit board of a peripheral circuit) due to an excessiverise in temperature resulting from heat which generates from a highexothermic element, such as a power semiconductor element, tend tobecome increasingly severe.

Therefore, in a high-capacity module which is intended to attainreduction in size and weight, reduction in surge, and reduction in aloss, by lamination of various composition circuit boards, a technology,which can more efficiently transmit heat which generates from a highexothermic element outside to reduce problems, such as breakage of themodule etc. (for example, degradation of sealing resin of a circuitelement which constitutes the module, and/or expansion and/ordeformation of a resin circuit board of a peripheral circuit) due to anexcessive rise in temperature while attaining reduction in size andweight, reduction in surge, and reduction in a loss, has been sought.

The present invention has been conceived in order to meet such a demand.More specifically, the present invention has an objective to provide ahighly reliable circuit board for a peripheral circuit which cantransmit heat which generates from a high exothermic element, such as apower semiconductor element, while attaining reduction in size andweight, reduction in surge, and reduction in a loss, in high-capacitymodules including power modules, such as an inverter.

Solution to Problem

The above-mentioned objective can be attained by,

a circuit board which is used for a second electronic circuit laminatedon the side of a first electronic circuit containing a high exothermicelement, on which said high exothermic element is disposed, via saidhigh exothermic element, characterized in that:

said circuit board comprises a substrate, which comprises dielectriclayer(s) mainly comprising ceramics, and first surface electrode(s),which is formed on the side of said circuit board, facing said firstelectronic circuit,

at least a part of conductor, which constitutes said first surfaceelectrode(s), is embedded inside of said substrate,

said conductor, which constitutes said first surface electrode(s), isexposed out of said substrate at least in a region of a first surfacewhich is the surface of said circuit board, facing said first electroniccircuit, and said region is opposed to terminal(s) of said highexothermic element, and

the thickness of said conductor, which constitutes said first surfaceelectrode(s), is not less than 100 micrometers in a directionperpendicular to said first surface.

Advantageous Effects of Invention

As mentioned above, a circuit board according to the present inventioncan be used in a (second) electronic circuit (for example, a peripheralcircuit, such as a drive circuit) which is laminated with a (first)electronic circuit (for example, a power circuit) containing a highexothermic element, for example, for the purpose of reduction in sizeand weight of a high-capacity module including a power module, such asan inverter, etc.

A circuit board according to the present invention has a configurationin which a first surface electrode formed on the side facing a firstelectronic circuit is disposed in a substrate comprising dielectriclayer(s) which mainly comprises ceramics. Thereby, when a secondelectronic circuit including the circuit board is laminated on the side,on which a high exothermic element of the first electronic circuitcontaining the high exothermic element is disposed, of the firstelectronic circuit, via the high exothermic element, it becomes possibleto release heat which generates from the high exothermic element notonly via the circuit board of the first electronic circuit, but also viathe circuit board of the second electronic circuit, and therefore heatrelease of the whole module containing these electronic circuits can beeffectively performed to suppress excessive rise in temperature of themodule.

Moreover, since ceramics has a smaller thermal expansion coefficient ascompared with resin widely used as a substrate of resin circuit boardsaccording to conventional technologies, stress resulting from heatgeneration from a high exothermic element (for example, a powersemiconductor element, etc.) as mentioned above due to difference ofthermal expansion coefficients of circuit boards between a peripheralcircuit (drive circuit) and a power circuit.

In addition to the above, in the circuit board according to the presentinvention, at least a part of conductor which constitutes the firstsurface electrode is embedded inside of the substrate. Thereby, a highlyreliable high-capacity module can be achieved, since stress acting on aninterface between the substrate and the conductor (such as, for example,stress which generates due to difference between thermal expansioncoefficients of the substrate and the conductor which constitutes thefirst surface electrode(s) and/or stress which generates due todifference between thermal expansion coefficients of the circuit boardaccording to the present invention and the high exothermic elementand/or the circuit board of the first electronic circuit, etc.) can bereduced.

Furthermore, in the circuit board according to the present invention,the conductor, which constitutes the first surface electrode(s), isexposed out of the substrate at least in a region of a first surfacewhich is the surface of said circuit board, facing said first electroniccircuit, and said region is opposed to a terminal(s) of said highexothermic element. Thereby, the second electronic circuit including thecircuit board according to the present invention and the high exothermicelement can be connected in a shorter distance, for example, to suppresssurge voltage at the time of switching (reduction in surge).

Still furthermore, in the circuit board according to the presentinvention, the thickness of the conductor, which constitutes the firstsurface electrode(s), is not less than 100 micrometers (in a directionperpendicular to the first surface). Thereby, the loss as the wholemodule including the electronic circuit which uses the circuit boardaccording to the present invention can be reduced.

As mentioned above, the present invention can provide a highly reliablecircuit board for a peripheral circuit which can more efficientlytransmit heat generating from a high exothermic element, such as a powersemiconductor element, outside while attaining reduction in size andweight, reduction in surge, and reduction in a loss, in high-capacitymodules including power modules, such as an inverter.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 A schematic view showing the configurations of a circuit boardaccording to one embodiment of the present invention and a modulecontaining the circuit board.

FIG. 2 A schematic view showing the configurations of a power moduleaccording to a conventional technology.

FIG. 3 A schematic view illustrating the difference in stresses actingon the interface between electrode(s) disposed at the surface of thecircuit board and the substrate of circuit boards according to oneembodiment of the present invention and a circuit board according to aconventional technology.

FIG. 4 A schematic view showing the configurations of a circuit boardaccording to one modification of an embodiment of the present invention,wherein a capacitor is embedded inside of a second electronic circuitboard, and a module containing the circuit board.

FIG. 5 A schematic view showing the configurations of a circuit boardaccording to another modification of an embodiment of the presentinvention, wherein a capacitor is embedded in a part of region(s) insideof a second electronic circuit board, and a module containing thecircuit board.

FIG. 6 A schematic view showing the configurations of a circuit boardaccording to still another modification of an embodiment of the presentinvention, wherein a capacitor is embedded within the layer nearest tothe first surface inside of a second electronic circuit board, and amodule containing the circuit board.

DETAILED DESCRIPTION OF THE INVENTION

As mentioned above, the present invention has an objective to provide ahighly reliable circuit board for a peripheral circuit which cantransmit heat which generates from a high exothermic element, such as apower semiconductor element, outside while attaining reduction in sizeand weight, reduction in surge, and reduction in a loss, inhigh-capacity modules including power modules, such as an inverter.

As a result of wholehearted research for achieving the above-mentionedobjective, the inventors have conceived that, in high-capacity modulesincluding power modules, such as an inverter, by laminating a peripheralcircuit using a ceramics circuit board within which an electrodeconstituted by thick conductor is embedded on an exothermic element,overheating of the module can be suppressed due to more effective heatrelease via the circuit board while attaining reduction in size andweight, reduction in surge, and reduction in a loss of the module.

Namely, the first embodiment of the present invention is;

A circuit board which is used for a second electronic circuit laminatedon the side of a first electronic circuit containing a high exothermicelement, on which said high exothermic element is disposed, via saidhigh exothermic element, characterized in that:

said circuit board comprises a substrate, which comprises dielectriclayer(s) mainly comprising ceramics, and first surface electrode(s),which is formed on the side of said circuit board, facing said firstelectronic circuit,

at least a part of conductor, which constitutes said first surfaceelectrode(s), is embedded inside of said substrate,

said conductor, which constitutes said first surface electrode(s), isexposed out of said substrate at least in a region of a first surfacewhich is the surface of said circuit board, facing said first electroniccircuit, and said region is opposed to terminal(s) of said highexothermic element, and

the thickness of said conductor, which constitutes said first surfaceelectrode(s), is not less than 100 micrometers in a directionperpendicular to said first surface.

As mentioned above, the circuit board according to the presentembodiment as a circuit board constituting a peripheral circuit (secondelectronic circuit) such as a drive circuit is laminated on the side, onwhich a high exothermic element such as a power semiconductor element isdisposed, of an electronic circuit (first electronic circuit) containingthe high exothermic element via the high exothermic element, tocontribute to reduction in size and weight of high-capacity (largeelectric power) modules including power modules, such as an inverter,

In addition, as mentioned above, the above-mentioned high-capacity(large electric power) modules may be power modules, such as aninverter, or may be other high-capacity modules handling large electricpower. Moreover, although power semiconductor elements, such as aswitching element, can be exemplified as the above-mentioned highexothermic element when the above-mentioned high-capacity (largeelectric power) modules are power modules, such as an inverter, asmentioned above, the high exothermic element in the present embodimentis not limited to a switching element, and it may be any element whichemits large quantities of heat in a high-capacity (large electric power)module. Furthermore, although an IGBT, an SiC-MOSFET, etc. can beexemplified as a switching element when the above-mentioned highexothermic element is a switching element, a switching element in thepresent embodiment is not limited to an IGBT and an SiC-MOSFET, and itmay be any switching element known in the art.

By the way, as mentioned previously, in a conventional technology, whenvarious circuit boards constituting a high-capacity module are laminatedas mentioned above, although the module can attain reduction in size andweight, It becomes more difficult to transmit and release outside heatgenerating from a power semiconductor element such as a switchingelement, and there is a possibility that problems such as breakage ofthe module (for example, degradation of sealing resin of the circuitelement constituting the module) etc. by excessive rise in temperaturedue to heat generation from these high exothermic elements.

Then, in a conventional technology, as a countermeasure against theproblems as mentioned above, for example, an attempt to transfer heatgenerating from a switching element via a leadframe to an upperdirection of the module (direction from the first electronic circuit tothe second electronic circuit) by pasting a leadframe on theundersurface of the circuit board of a drive circuit (corresponding tothe second electronic circuit) laminated on a power circuit(corresponding to the first electronic circuit) containing a switchingelement has been also proposed (for example, refer to Patent Literature1 (PTL 1)). However, in such a configuration, since the pathway to theupper direction of the heat generating from the switching element islimited to the leadframe, there is a possibility that the heatdissipation effect may become insufficient. Moreover, since circuitboards for peripheral circuits according to a conventional technologyare made of resin in many cases and its thermal conductivity is low,sufficient heat dissipation through the circuit board of a peripheralcircuit cannot be expectable.

On the other hand, as mentioned above, the circuit board according tothe present embodiment has a configuration in which the first surfaceelectrode(s) formed on the side of the first electronic circuit isdisposed in the substrate comprising dielectric layer(s) which mainlycomprises ceramics. Thereby, in a module where the circuit boardaccording to the present embodiment as a circuit board of a secondelectronic circuit is laminated on the side of the high exothermicelement of the first electronic circuit through the high exothermicelement, it becomes possible to release heat which generates from thehigh exothermic element not only via the circuit board of the firstelectronic circuit, but also via the circuit board according to thepresent embodiment, which has higher thermal conductivity as comparedwith the circuit board of a peripheral circuit according to aconventional technology, to the side of the second electronic circuit,and thus heat in the whole module including these electronic circuitscan be effectively released, and thereby excessive rise in temperatureof the module can be suppressed.

In addition, as mentioned above, at least a part of the conductor, whichconstitutes the first surface electrode(s), is embedded inside of thesubstrate of the circuit board of the second electronic circuit.Therefore, a state where at least a part of the conductor, whichconstitutes the first surface electrode(s), is embedded inside of thesubstrate and the other parts protrude from the first surface, which isthe surface of the circuit board of the second electronic circuit,facing the first electronic circuit can be assumed. In such a state, acase where the substrate of the circuit board of the second electroniccircuit does not contact the high exothermic element and only theconductor which constitutes the first surface electrode(s) contacts thehigh exothermic element on the first electronic circuit may happen.However, even in such a case, heat which generates from the highexothermic element is transmitted to the substrate of the circuit boardof the second electronic circuit via the protruded first surfaceelectrode(s). In addition, since the substrate of the circuit boardaccording to the present embodiment comprises dielectric layer(s) mainlycomprising ceramics, as mentioned above, it has higher thermalconductivity as compared with the circuit board of the peripheralcircuit according to a conventional technology. As a result, even insuch a case, the circuit board according to the present embodiment canrelease heat more effectively as compared with the circuit board of theperipheral circuit according to a conventional technology.

On the other hand, a state where the whole conductor, which constitutesthe first surface electrode(s), is embedded inside of the substrate andonly the surface of the conductor is exposed in the same plane as thefirst surface of the circuit board can be also assumed. In such a state,both of the surface of the substrate of the second electronic circuitand the surface of the conductor which constitutes the first surfaceelectrode(s) can be simultaneously contacted with the high exothermicelement. In this case, heat which generates from the high exothermicelement is transmitted, from a portion which directly contacts theconductor of the first surface electrode(s) (for example, a terminalportion of the high exothermic element concerned, etc.) to theconductor, and from a portion which contacts the substrate of thecircuit board of the second electronic circuit to the substrate,respectively.

In the point that heat thus transmitted to the circuit board accordingto the present embodiment is released via the circuit board thereafter,the above state is the same as the state where the conductor whichconstitutes the first surface electrode(s) protrudes from the firstsurface. However, in the state where only the surface of the conductorwhich constitutes the first surface electrode(s) is exposed in the sameplane as the first surface, as mentioned above, since the contact areabetween the high exothermic element and the circuit board of the secondelectronic circuit becomes large, heat can be released much moreeffectively.

In addition, as a modification of the present embodiment, unless itbecomes a substantial hindrance of reduction in the size and weight,reduction in surge, and reduction in a loss in a high-capacity module,an electrical connection with the high exothermic element may beachieved through a leadframe etc. pasted to the first surfaceelectrode(s).

By the way, as mentioned above, the circuit board according to thepresent embodiment has a configuration wherein first surfaceelectrode(s) formed on the side of the first electronic circuit in thesubstrate which comprises dielectric layer(s) mainly comprisingceramics. As compared with resin generally used as a substrate of resincircuit boards according to a conventional technology, in general, thethermal expansion coefficient of ceramics is smaller. Thereby, when thecircuit board according to the present embodiment is used, for example,stress which generates due to the difference in the thermal expansioncoefficient of a circuit board between a peripheral circuit (drivecircuit) and a power circuit by heat generation from a high exothermicelement (for example, a power semiconductor element) etc. can be madesmaller as compared with the case where a resin circuit board accordingto a conventional technology is used.

In addition to the above, in the circuit board according to the presentembodiment, at least a part of the conductor, which constitutes thefirst surface electrode(s), is embedded inside of the substrate, asmentioned above. Thereby, stress which acts on the interface between theconductor and the substrate, such as stress which generates due to thedifference in thermal expansion coefficient between the conductorconstituting the electrode and the substrate, etc. can be reduced, andtherefore a highly reliable high-capacity module can be achieved.

More particularly, for example, when a leadframe and/or a conductivepattern are pasted on the surface of a circuit board like a circuitboard for a peripheral circuit according to a conventional technology,there is a possibility that stress which generates due to the differencein thermal expansion coefficient of circuit board between the peripheralcircuit (drive circuit) and a power circuit by heat generation from ahigh exothermic element as mentioned above (for example, a powersemiconductor element, etc.) may concentrate, for example, on theinterface between an electrode and (the substrate of) the circuit boardto separate the leadframe and/or a conductive pattern from the surfaceof the circuit board and lead to decrease in reliability of the wholemodule including the circuit or lead to disconnection and destruction ofthe circuit at worst.

In contrast to this, in the circuit board according to the presentembodiment, at least a part of the conductor, which constitutes firstsurface electrode(s) is embedded inside of the substrate. Thereby, sincethe surroundings of a point on which stress as mentioned aboveconcentrates are covered with the substrate of the circuit board andthereby the stress concerned is relaxed and distributed, unlike the casewhere a leadframe and/or a conductive pattern are pasted on the surfaceof a circuit board, for example, problems as mentioned above areunlikely to occur, and reliability as the whole module including anelectronic circuit which uses the circuit board can be further improved.

Furthermore, in the circuit board according to the present embodiment,the conductor, which constitutes first surface electrode(s), is exposedout of the substrate at least in a region of a first surface which isthe surface of the circuit board, facing the first electronic circuit,and the region is opposed to a terminal(s) of the high exothermicelement. Thereby, the second electronic circuit containing the circuitboard according to the present embodiment and the high exothermicelement can be connected in the shortest distance and therefore, forexample, surge voltage at the time of switching can be suppressed(reduction in surge).

More particularly, in the circuit board according to the presentembodiment, as mentioned above, the conductor, which constitutes thefirst surface electrode(s), is exposed out of the substrate so that itmay protrude from the first surface, which is the surface on the side ofthe circuit board, facing the first electronic circuit, or so that it isexposed in the same plane as the first surface. The conductor whichconstitutes the first surface electrode(s) electrically connects thesecond electronic circuit containing the circuit board according to thepresent embodiment with the high exothermic element. Namely, theconductor is exposed out of the substrate of the circuit board, at leastin a region of the first surface of the circuit board according to thepresent embodiment, which is opposed to a terminal(s) of the highexothermic element. Thereby, the second electronic circuit containingthe circuit board according to the present embodiment can be directlyconnected with the high exothermic element.

Therefore, in accordance with the present embodiment, the secondelectronic circuit and the high exothermic element can be connected in ashorter distance, as compared with the case where a peripheral circuitaccording to a conventional technology. As a result, inductance betweenthe first electronic circuit (for example, power circuit) containing thehigh exothermic element (for example, power semiconductor elements, suchas a switching element) and the second circuit (for example, peripheralcircuit, such as a drive circuit) containing the circuit board accordingto the present embodiment can be made smaller, and thereby, in a module(for example, a power module etc.) including these circuits, forexample, surge voltage at the time of switching can be suppressed(reduction in surge).

In addition, although the electrical connection between the conductorwhich constitutes the first electrode(s) exposed out of the substrate ofthe circuit board according to the present embodiment and the terminalof the high exothermic element can be achieved, for example, bysoldering, the connection methods are not limited to a specifictechnique, and the electrical connection between the conductor whichconstitutes the first electrode(s) and the terminal of the highexothermic element may be achieved by using any of the techniques knownin the art.

Furthermore, in the circuit board according to the present embodiment,the thickness of the conductor, which constitutes the first surfaceelectrode(s), is not less than 100 micrometers, more preferably not lessthan 200 micrometers (in a direction perpendicular to the firstsurface). Thereby, the loss as the whole module including an electroniccircuit which uses the circuit board according to the present embodimentcan be decreased.

As mentioned above, the first surface electrode(s) in the circuit boardaccording to the present embodiment electrically connects the secondelectronic circuit (for example, a peripheral circuit, such as a drivecircuit) containing the circuit board according to the presentembodiment with the high exothermic element (for example, powersemiconductor elements, such as a switching element) contained in thefirst electronic circuit (for example, power circuit). Therefore, sinceit is assumed that large current flows through the first surfaceelectrode(s), in order to make the loss in the first surfaceelectrode(s) smaller, it is desirable to enlarge the connection areabetween the high exothermic element and the first surface electrode(s).Similarly, it is also desirable to enlarge the thickness of theconductor which constitutes the first surface electrode(s).

As mentioned above, in accordance with the present embodiment, a highlyreliable circuit board for a peripheral circuit which can moreefficiently transmit heat generating from a high exothermic element,such as a power semiconductor element, outside while attaining reductionin size and weight, reduction in surge, and reduction in a loss, inhigh-capacity modules including power modules, such as an inverter canbe provided.

By the way, as long as the above-mentioned requirements are satisfied, amethod for manufacturing the circuit board according to the presentembodiment may be any kind of method, and can be suitably chosen fromvarious methods used for manufacturing ceramics circuit boards in theart. As a specific example of the method for manufacturing the circuitboard according to the present embodiment, for example, what is called a“gel-cast method”, a “doctor blade method”, etc. can be exemplified.

When the above-described gel-cast method is adopted, a circuit boardaccording to the present embodiment can be obtained, for example, bydisposing a conductive pattern on the surface of a film-like orsheet-like protective backing material by a printing method, such as ascreen printing method, etc., injecting a slurry of a dielectricmaterial, such as ceramics, into the portion in which the conductivepattern has not been disposed, laminating required number of sheets of adielectric material with the conductive pattern embedded therein, whichis obtained by solidifying the slurry to constitute the conductivepattern as surface electrode(s), and sintering the same.

As the above-mentioned protective backing material, it is desirable touse resin films, such as a polyethylene terephthalate (PET) film, apolyethylene naphthalate (PEN) film and, besides resin films, variousfilm-like or sheet-like materials, such as a glass board, paper, ormetal, can be used. However, as protective backing material, it ispreferable to use those with flexibility from a viewpoint of the ease ofpeel-off operation.

Moreover, for example, for the objective of enabling it to easily peeloff the sheet of the dielectric material from the protective backingmaterial, etc., for example, a release agent etc. may be applied to thesurface of the above-mentioned protective backing material. Such arelease agent includes, for example, various agents known as moldlubricant in the art. More specifically, as such a release agent,well-known silicone series release agents, fluorine series releaseagents, and etc. can be used.

It is desirable that the above-mentioned conductive pattern is disposedby forming a conductive paste, which comprises, as main components, atleast one or more kinds of metal chosen from, for example, gold (Au),silver (Ag), and copper (Cu), etc. and a thermosetting resin precursor,on the surface of the above-mentioned protective backing material, by amethod, such as a screen printing, etc. As such thermosetting resinprecursors, phenol resin, resole resin, urethane resin, epoxy resin,melamine resin, etc. can be used. Among these, phenol resin and resoleresin are especially preferable. After printing such a conductive pasteon the surface of the above-mentioned protective backing material, aconductive pattern can be obtained by hardening the binder contained inthe conductive paste.

As slurry of the above-mentioned dielectric material, for example,slurry which comprises resin, ceramics powder, and a solvent can beexemplified. In this case, resin can function as what is called a“binder” and, for example, thermosetting resin, such as phenol resin,resole resin, or polyurethane resin, or a polyurethane precursor whichcomprises polyol and polyisocyanate can be used. Among these, athermosetting resin precursor which comprises polyol and polyisocyanateis especially preferable.

As a ceramics material used as ceramics powder, any of oxide seriesceramics or non-oxide series ceramics can be used. For example, alumina(Al₂O₃), zirconia (ZrO₂), barium titanate (BaTiO₃), silicon nitride(Si₃N₄), silicon carbide (SiC), barium oxide (BaO), titanium oxide(TiO₂), oxidized silicon (SiO₂), zinc oxide (ZnO₂), neodymium oxide(Nd₂O₃), etc. can be used. Moreover, these materials may be used solelyor in combination of two or more kinds thereof. Furthermore, as long asa slurry can be prepared, particle size of ceramics material is notparticularly limited.

Moreover, the above-mentioned solvent is not particularly limited, aslong as it can dissolve resin as the above-mentioned binder (and adispersing agent, when used). As a specific example of the solvent, asolvent which has two or more ester bonds, such as polybasic acid ester(for example, dimethyl glutarate, etc.) and acid ester of polyhydricalcohol (for example, triacetin (glyceryl triacetate) etc.), etc, can beexemplified.

Furthermore, slurry of the above-mentioned dielectric material maycontain a dispersing agent in addition to the above-mentioned resin,ceramics powder, and solvent. As a specific example of a dispersingagent, for example, polycarboxylic acid series copolymers,polycarboxylic acid salts, etc. can be exemplified. By adding such adispersing agent, a slurry before molding can have low viscosity andhigh flowability.

By the way, various current, such as a signal for controlling operationof a high exothermic element, an input current to a high exothermicelement, or output current from a high exothermic element, for example,may flow through various circuit element(s) and terminal(s) whichconstitute the second electronic circuit containing the circuit boardaccording to the present invention. These current flows via theabove-mentioned first surface electrode(s) between various circuitelement(s), terminal(s), etc, which constitute the second electroniccircuit, and a high exothermic element. However, it is common thatvarious circuit element(s) and terminal(s), etc. which constitute thesecond electronic circuit are disposed on the surface opposite to thefirst surface electrode(s) of the circuit board according to the presentinvention. Therefore, a circuit which electrically connects the firstsurface electrode(s) with various circuit element(s), terminal(s), etc.disposed on the surface of the opposite side of the circuit board isrequired.

Such an electrical connection can be achieved by at least one layer ofinner layer electrode(s) embedded inside of the circuit board accordingto the present invention. Since an electrical connection through such aninner layer electrode(s) between the first surface electrode(s) andvarious circuit elements, terminal, etc. which are disposed on thesurface on the side opposite to the circuit board can be made shorter ascompared with a connection method according to a conventionaltechnology, for example, such as wire bonding, and therefore can reducethe loss as the whole module including the electronic circuit which usesthe circuit board according to the present invention, it is desirable.

Therefore, the second embodiment of the present invention is;

a circuit board which is used for a second electronic circuit laminatedon the side of a first electronic circuit containing a high exothermicelement, on which said high exothermic element is disposed, via saidhigh exothermic element, characterized in that:

said circuit board comprises a substrate, which comprises dielectriclayer(s) mainly comprising ceramics, and first surface electrode(s),which is formed on the side of said circuit board, facing said firstelectronic circuit, and at least one layer of inner layer electrode(s),which is embedded inside of inner layer(s) of said circuit board,

at least a part of conductor, which constitutes said first surfaceelectrode(s), is embedded inside of said substrate,

said conductor, which constitutes said first surface electrode(s), isexposed out of said substrate at least in a region of a first surfacewhich is the surface of said circuit board, facing said first electroniccircuit, and said region is opposed to terminal(s) of said highexothermic element, and

the thicknesses of said conductor, which constitutes said first surfaceelectrode(s), and conductor, which constitutes at least one layer ofsaid inner layer electrode(s), are not less than 100 micrometers in adirection perpendicular to said first surface.

The circuit board according to the present embodiment has the sameconfiguration as the circuit board according to said first embodiment ofthe present invention, except for that the circuit board furthercomprises at least one layer of the inner layer electrode(s) embeddedinside of an inner layer of the circuit board and the thickness of theconductor which constitutes at least one layer of the inner layerelectrode(s) in a direction which intersects perpendicularly with thefirst surface is not less than 100 micrometers. In the presentembodiment, as mentioned above, not only the conductor which constitutesthe first surface electrode(s), but also the conductor which constitutesat least one layer of the inner layer electrode(s) have thicknesses ofnot less than 100 micrometers, more preferably not less than 200micrometers (in a direction which intersects perpendicularly with thefirst surface). Thereby, in the circuit board according to the presentembodiment, the loss in the electrical connection between variouscircuit element(s), terminal(s), etc. which constitute the secondelectronic circuit, and the high exothermic element can be also madesmaller, and as a result the loss as the whole module including theelectronic circuit which uses the circuit board according to the presentembodiment can be made small.

By the way, as mentioned above, in the circuit board according to thepresent embodiment, the thicknesses of the conductor, which constitutesthe first surface electrode(s), and the conductor, which constitutes atleast one layer of the inner layer electrode(s), (in a directionperpendicular to the first surface) are not less than 100 micrometers,more preferably not less than 200 micrometers. Thereby, the loss as thewhole module including the electronic circuit which uses the circuitboard according to the present embodiment can be made small.

Moreover, as mentioned above, the first surface electrode(s) in thecircuit board according to the present embodiment electrically connectsthe second electronic circuit (for example, a peripheral circuit, suchas a drive circuit) containing the circuit board according to thepresent embodiment with the high exothermic element (for example, powersemiconductor elements, such as a switching element) contained in thefirst electronic circuit (for example, power circuit). Therefore, sinceit is assumed that large current flows through the first surfaceelectrode(s), in order to make the loss in the first surfaceelectrode(s) smaller, it is desirable to enlarge the connection areabetween the high exothermic element and the first surface electrode(s).As a result, the total area which the first surface electrode(s)occupies in the first surface of the circuit board according to thepresent embodiment becomes larger.

On the other hand, at the surface on the side opposite to the firstsurface of the circuit board according to the present embodiment (thesecond surface), electrode(s) for mounting various circuit elements,which constitute the second electronic circuit containing the circuitboard according to the present embodiment, and/or terminals, etc. (thesecond surface electrode(s)) (for example, land etc.) is disposed inmany cases. The second electronic circuit constitutes a peripheralcircuit, such as a drive circuit, etc., as mentioned above. Therefore,unlike the first surface electrode(s) for achieving a (high-capacity)electrical connection with the high exothermic element, the secondsurface electrode(s) comes to achieve an electrical connection with arelatively low-capacity (low electric power) circuit elements whichconstitute a peripheral circuit, and therefore the total area which thesecond surface electrode(s) occupies in the second surface of thecircuit board according to the present embodiment becomes relativelysmaller and the thickness of the conductor which constitutes the secondsurface electrode(s) (in a direction which intersects perpendicularlywith the first surface) also becomes relatively thinner.

As mentioned above, in the circuit board according to the presentembodiment, the total area which the first surface electrode(s) occupiesin the first surface facing the first electronic circuit containing thehigh exothermic element is relatively large, and the thickness of thefirst surface electrode(s) is also relatively thick. On the other hand,the total area which the second surface electrode(s) occupies in thesecond surface on the side opposite to the first surface, on whichvarious circuit elements constituting the second electronic circuitand/or terminals, etc. are mounted, is relatively small, and thethickness of the second surface electrode(s) is also relatively thin. Asmentioned above, the material which constitutes these electrodescomprises metal as a major component and has a larger thermal expansioncoefficient as compared with the dielectric material comprising ceramicsas a major component, which is the substrate of the circuit boardaccording to the present embodiment. Namely, the total area which theelectrode(s) having a larger thermal expansion coefficient occupies andthe thickness thereof are relatively large on the first surface side ofthe circuit board according to the present embodiment, while the totalarea which the electrode(s) having a larger thermal expansioncoefficient occupies and the thickness thereof are relatively small onthe second surface side of the circuit board according to the presentembodiment.

Moreover, in general, the cross-sectional area by a plane parallel tothe first surface of the conductor which constitutes at least one layerof the inner layer electrode(s) embedded inside the substrate of thecircuit board according to the present embodiment is also smaller thanthe total area of the first surface electrode(s).

Therefore, for example, when the temperature of the circuit boardaccording to the present embodiment rises due to heat generation fromthe high exothermic element in accordance with operation of the modulewhich comprises the second electronic circuit containing the circuitboard and the first electronic circuit containing the high exothermicelement, the extent of thermal expansion resulting from the rise intemperature is different between the region in the vicinity of the firstsurface of the circuit board according to the present embodiment andother regions. More specifically, the extent of thermal expansion of theregion in the vicinity of the first surface, where the total area andthickness occupied by the first surface electrode(s) are relativelylarge, becomes larger as compared with the extent of thermal expansionof other regions (where the total area and thickness occupied byelectrode(s) are relatively small).

Due to the difference in the extent of thermal expansion between theregion in vicinity of the first surface and other regions, the circuitboard according to the present embodiment may be curved when thetemperature of the circuit board according to the present embodimentremarkably changes. For example, in the cooling process aftermanufacturing the circuit board according to the present embodiment bysintering as mentioned above, the extent of contraction of the region invicinity of the first surface of the circuit board accompanying thetemperature fall is relatively large, and the extent of contraction ofother regions of the circuit board is relatively small. Consequently,even if the circuit board is not curved at the time of the completion ofsintering, the circuit board may be curved so that the first surfaceside may become concave, as a result of the above-mentioned temperaturefall.

Moreover, even if a circuit board without a curvature is obtained at thetime of the completion of cooling (that is, at the time of thecompletion of manufacture of the circuit board), for example, byelaborating a countermeasure such as sintering in a state where thecircuit board is curved beforehand so that the curvature accompanyingcooling after sintering as mentioned above may be offset, for example,when the rise in temperature resulting from heat generation from thehigh exothermic element in accordance with operation of the module whichcomprises the second electronic circuit containing the circuit boardaccording to the present embodiment and the first electronic circuitcontaining the high exothermic element is remarkable, the extent ofexpansion of the region in vicinity of the first surface of the circuitboard accompanying the rise in temperature is relatively large, and theextent of expansion of other regions of the circuit board is relativelysmall. Consequently, even if the circuit board is not curved at the timeof the completion of manufacture, the circuit board may be curved sothat the first surface side may become convex as a result of theabove-mentioned rise in temperature.

When the circuit board according to the present embodiment is curved asmentioned above, contact and junction between the circuit boardaccording to the present embodiment and the high exothermic element arenot fully secured and, as a result, there is a possibility thattransmission to the circuit board of heat which generates from the highexothermic element may become insufficient, the electrical connectionbetween the high exothermic element and the second electronic circuitmay be shut off, and the electrical connection between the circuitelements which constitute the second electronic circuit may be shut off.

As mentioned above, in the circuit board according to the presentembodiment, the volume occupied by the electrode(s) having a largerthermal expansion coefficient (as compared with the substrate of thecircuit board) is relatively large in the region in vicinity of thefirst surface, while the volume occupied by the electrode(s) having alarger thermal expansion coefficient (as compared with the substrate ofthe circuit board) is relatively small in other regions. Therefore, itis thought that the above-mentioned curvature may occur due to theaverage thermal expansion coefficient of the region in vicinity of thefirst surface being larger than the average thermal expansioncoefficient of other regions.

Therefore, in order to suppress generating of the curvature as mentionedabove, it is thought desirable to make small the difference between theaverage thermal expansion coefficient of the region in vicinity of thefirst surface of the circuit board according to the present embodimentand the average thermal expansion coefficient of other regions. Fromsuch a viewpoint, as a result of wholehearted research, the inventorshave found that the curvature of the circuit board, as mentioned above,can be suppressed by making the thickness of the conductor whichconstitutes at least one layer of the inner layer electrode(s) largerthan the thickness of the conductor which constitutes the first surfaceelectrode(s).

Namely, the third embodiment of the present invention is;

the circuit board according to said second embodiment of the presentinvention, characterized in that:

the thickness of said conductor, which constitutes at least one layer ofsaid inner layer electrode(s), in a direction perpendicular to saidfirst surface is larger than the thickness of said conductor, whichconstitutes said first surface electrode(s), in a directionperpendicular to said first surface.

In the circuit board according to the present embodiment, as mentionedabove, the thickness (in a direction perpendicular to the first surface)of the conductor which constitutes at least one layer of the inner layerelectrode(s) is larger than the thickness (in a direction perpendicularto the first surface) of the conductor which constitutes the firstsurface electrode(s). Thereby, as compared with the case where thethickness of the conductor which constitutes the inner layerelectrode(s) is comparable to or smaller than the thickness of theconductor which constitutes the first surface electrode(s), the averagethermal expansion coefficient of the region which contains the innerlayer electrode and is not in vicinity of the first surface becomeslarger. As a result, as compared with the case where the thickness ofthe conductor which constitutes the inner layer electrode(s) iscomparable to or smaller than the thickness of the conductor whichconstitutes the first surface electrode(s), the difference of theaverage thermal expansion coefficient of the region in vicinity of thefirst surface and the thermal expansion coefficient of other regionsbecomes smaller.

In addition, the thickness of the conductor which constitutes at leastone layer of the inner layer electrode(s) in the circuit board accordingto the present embodiment can be determined, for example, according tothe total area and/or thickness of the conductor which constitutes thefirst surface electrode(s), the total area of the inner layerelectrode(s) and/or the position at which the inner layer electrode(s)is embedded inside the circuit board, etc., so that the extent ofcurvature of the circuit board in a temperature range to which thecircuit board is subjected in its intended use may be fall within anacceptable range in the use. Namely, the thickness of the conductorwhich constitutes at least one layer of the inner layer electrode(s) inthe circuit board according to the present embodiment can be suitablydetermined according to the acceptable range of the curvature of thecircuit board in the usage environment and/or intended use of the modulecontaining the circuit board, the configuration and/or arrangement ofvarious electrodes in the circuit board, etc.

As mentioned above, in the circuit board according to the presentembodiment, since the difference of the average thermal expansioncoefficient of the region in vicinity of the first surface and thethermal expansion coefficient of other regions can be made smaller, thecurvature of the circuit board according to the present embodiment canbe reduced even when the temperature of the circuit board changesremarkably.

As a result, in the circuit board according to the present embodiment,inconveniences that, due to the curvature of the circuit board, asmentioned above, contact and junction between the circuit board and thehigh exothermic element may become insufficient, transmission to thecircuit board of heat which generates from the high exothermic elementmay become insufficient, the electrical connection between the highexothermic element and the second electronic circuit may be shut off,and the electrical connection between the circuit elements whichconstitute the second electronic circuit may be shut off, etc. can besuppressed.

As mentioned above, as concrete measures for making small the differenceof the average thermal expansion coefficient of the region in vicinityof the first surface and the average thermal expansion coefficient ofother regions in the circuit board according to the present inventionfor the purpose of suppressing the generation of curvature of thecircuit board accompanying a temperature change, it can be exemplifiedto make the thickness of the conductor which constitutes at least onelayer of the inner layer electrode(s) contained in the circuit boardaccording to the second embodiment of the present invention larger thanthe thickness of the conductor which constitutes the first surfaceelectrode(s).

However, measures other than the above can make small the difference ofthe average thermal expansion coefficient of the region in vicinity ofthe first surface and the average thermal expansion coefficient of otherregions in the circuit board according to the present invention. Forexample, the thermal expansion coefficient of the substrate of thecircuit board according to the present invention may be configured sothat that on the second surface side may become higher than the firstsurface side. Specifically, for example, the dielectric layer whichconstitutes the substrate of the circuit board according to the presentinvention may be formed by plural dielectric layers and it may beconfigured so that, among these plural dielectric layers, the thermalexpansion coefficient of the dielectric layer which forms the secondsurface that is the surface on the side opposite to the first surfacemay become larger than the thermal expansion coefficient of thedielectric layer which forms the first surface. Thereby, as mentionedabove, even if the volume ratio occupied by the electrode(s) with alarge thermal expansion coefficient is relatively large in the region invicinity of the first surface while that is relatively small in otherregions, the difference of the average thermal expansion coefficient ofthe region in vicinity of the first surface and the average thermalexpansion coefficient of other regions can be suppressed to be smaller.

Namely, the fourth embodiment of the present invention is;

the circuit board according to any one of said first embodiment to saidthird embodiment of the present invention, characterized in that:

said dielectric layer(s) is formed of plural dielectric layers, and

among said plural dielectric layers, a dielectric layer forming a secondsurface which is a surface opposite to said first surface has a thermalexpansion coefficient larger than that of a dielectric layer formingsaid first surface.

As mentioned above, in the circuit board according to the presentembodiment, the dielectric layer(s) is formed of plural dielectriclayers and it is configured so that, among these plural dielectriclayers, a dielectric layer forming a second surface which is a surfaceopposite to the first surface has a thermal expansion coefficient largerthan that of a dielectric layer forming the first surface. Thereby, asmentioned above, even if the volume ratio occupied by the electrode(s)with a large thermal expansion coefficient is relatively large in theregion in vicinity of the first surface while that is relatively smallin other regions, the difference of the average thermal expansioncoefficient between the region in vicinity of the first surface andother regions resulting from such volume ratios of the electrode(s) canbe at least partially offset with the difference of the thermalexpansion coefficient between the dielectric layers which constitute thesubstrate of the circuit board. As a result, in the circuit boardaccording to the present embodiment, the difference of the averagethermal expansion coefficient of the region in vicinity of the firstsurface and the average thermal expansion coefficient of other regionscan be suppressed to be smaller.

As mentioned above, also in the circuit board according to the presentembodiment, since the difference of the average thermal expansioncoefficient of the region in vicinity of the first surface and thethermal expansion coefficient of other regions can be made smaller, thecurvature of the circuit board according to the present embodiment canbe reduced even when the temperature of the circuit board changesremarkably.

As a result, also in the circuit board according to the presentembodiment, inconveniences that, due to the curvature of the circuitboard, as mentioned above, contact and junction between the circuitboard and the high exothermic element may become insufficient,transmission to the circuit board of heat which generates from the highexothermic element may become insufficient, the electrical connectionbetween the high exothermic element and the second electronic circuitmay be shut off, and the electrical connection between the circuitelements which constitute the second electronic circuit may be shut off,etc. can be suppressed.

By the way, as mentioned above, the present invention relates to acircuit board for peripheral circuits of high-capacity modules. Moreparticularly, the present invention relates to a circuit board forperipheral circuits to be laminated with a circuit containing a highexothermic element in high-capacity modules including power modules,such as an inverter used in a hybrid car or an electric vehicle, etc.(via the high exothermic element). Furthermore, the present inventionalso relates to a high-capacity module including a peripheral circuitwhich uses the circuit board.

Herein, as mentioned above, a high-capacity module refers to a modulehandling a large electric power, including power modules, such as aninverter, etc. As for such a high-capacity module, as mentioned above,for example, along with the popularization of hybrid cars and ofelectric vehicles etc., further reduction in size and weight as well asstill higher-efficiency has been increasingly strongly demanded.

In order to meet the above-mentioned demand, it is desirable to use thecircuit board according to the present invention in a peripheral circuitcontained in a high-capacity module. Thereby, in such a high-capacitymodule, while reduction in size and weight, reduction in surge, andreduction in a loss of the module are achieved, heat which generatesfrom the high exothermic elements, such as a power semiconductorelement, can be transmitted more efficiently outside, and reliability asthe whole module can be further improved. Therefore, high-capacitymodules containing a peripheral circuit using the circuit boardaccording to any one of said first embodiment to said fourth embodimentas well as various other modifications of the present invention is alsoincluded in the scope of the present invention.

Namely, the fifth embodiment of the present invention is;

a high-capacity module which comprises a first electronic circuitcontaining a high exothermic element, and a second electronic circuitlaminated through said high exothermic element on the side, on whichsaid high exothermic element is disposed, of said first electroniccircuit, characterized in that:

a circuit board used for said second electronic circuit comprises asubstrate, which comprises dielectric layer(s) mainly comprisingceramics, and first surface electrode(s), which is formed on the side ofsaid circuit board, facing said first electronic circuit,

at least a part of conductor, which constitutes said first surfaceelectrode(s), is embedded inside of said substrate,

said conductor, which constitutes said first surface electrode(s), isexposed out of said substrate at least in a region of a first surfacewhich is the surface of said circuit board, facing said first electroniccircuit, and said region is opposed to a terminal(s) of said highexothermic element, and

the thicknesses of said conductor, which constitutes said first surfaceelectrode(s), is not less than 100 micrometers in a directionperpendicular to said first surface.

Moreover, the sixth embodiment of the present invention is;

a high-capacity module which comprises a first electronic circuitcontaining a high exothermic element, and a second electronic circuitlaminated through said high exothermic element on the side, on whichsaid high exothermic element is disposed, of said first electroniccircuit, characterized in that:

a circuit board used for said second electronic circuit comprises asubstrate, which comprises dielectric layer(s) mainly comprisingceramics, and first surface electrode(s), which is formed on the side ofsaid circuit board, facing said first electronic circuit, and at leastone layer of inner layer electrode(s), which is embedded inside of innerlayer(s) of said circuit board,

at least a part of conductor, which constitutes said first surfaceelectrode(s), is embedded inside of said substrate,

said conductor, which constitutes said first surface electrode(s), isexposed out of said substrate at least in a region of a first surfacewhich is the surface of said circuit board, facing said first electroniccircuit, and said region is opposed to a terminal(s) of said highexothermic element, and

the thicknesses of said conductor, which constitutes said first surfaceelectrode(s), and conductor, which constitutes at least one layer ofsaid inner layer electrode(s), are not less than 100 micrometers in adirection perpendicular to said first surface.

Furthermore, the seventh embodiment of the present invention is;

the high-capacity module according to said sixth embodiment of thepresent invention, characterized in that:

the thickness of said conductor, which constitutes at least one layer ofsaid inner layer electrode(s), in a direction perpendicular to saidfirst surface is larger than the thickness of said conductor, whichconstitutes said first surface electrode(s), in a directionperpendicular to said first surface.

Furthermore, the eighth embodiment of the present invention is;

the high-capacity module according to any one of said fifth embodimentto said seventh embodiment of the present invention, characterized inthat:

said dielectric layer(s) is formed of plural dielectric layers, and

among said plural dielectric layers, a dielectric layer forming a secondsurface which is a surface opposite to said first surface has a thermalexpansion coefficient larger than that of a dielectric layer formingsaid first surface.

In the high-capacity module according to any one of said fourthembodiment or said fifth embodiment of the present invention, the secondelectronic circuit using the circuit board according to any one of saidfirst embodiment or said second embodiment of the present invention,respectively, is laminated through the high exothermic element on theside of the high exothermic element of the first electronic circuit.Thereby, since it becomes possible for heat which generates from thehigh exothermic element to be released not only via the circuit board ofthe first electronic circuit, but also via the circuit board of thesecond electronic circuit, heat dissipation of the whole high-capacitymodule according to any one of said fourth embodiment or said fifthembodiment of the present invention can be performed effectively, andoverheating of the module can be suppressed.

Moreover, as mentioned above, in the circuit board according to saidfirst embodiment or said second embodiment of the present invention,since at least a part of the conductor which constitutes the firstsurface electrode(s) embedded inside of the substrate, the stress whichacts on the interface between the conductor and the substrate (forexample, stress which generates due to the difference in the thermalexpansion coefficient between the conductor, which constitutes theelectrode(s), and the substrate) is relaxed and reduced, and thereliability of the high-capacity module according to any one of saidfourth embodiment or said fifth embodiment of the present invention isimproved.

Furthermore, as mentioned above, in the circuit board according to anyone of said first embodiment or said second embodiment of the presentinvention, the conductor which constitutes the first surfaceelectrode(s) is exposed out of the substrate at least in the region ofthe first surface which is the surface of the circuit board, facing thefirst electronic circuit, and the region is opposed to the terminal(s)of the high exothermic element. Thereby, in the high-capacity moduleaccording to any one of said fourth embodiment or said fifth embodimentof the present invention, since the second electronic circuit can beconnected with the high exothermic element in a shorter distance, forexample, the surge voltage at the time of switching can be suppressed(reduction in surge).

Furthermore, in the circuit board according to any one of said firstembodiment or said second embodiment of the present invention, thethicknesses of the conductor, which constitutes the first surfaceelectrode(s), and the conductor, which constitutes at least one layer ofthe inner layer electrode(s) (included in the circuit board according tosaid second embodiment of the present invention), are not less than 100micrometers, more preferably not less than 200 micrometers (in adirection perpendicular to the first surface). Thereby, the loss as thewhole high-capacity module according to any one of said fourthembodiment or said fifth embodiment of the present invention can be madesmaller.

As mentioned above, in the high-capacity module according to any one ofsaid fifth embodiment to said eighth embodiment of the presentinvention, heat generating from a high exothermic element, such as apower semiconductor element, can be more efficiently transmittedoutside, while attaining reduction in size and weight, reduction insurge, and reduction in a loss. In accordance with such aspects, thehigh-capacity module according to any one of said fifth embodiment tosaid eighth embodiment of the present invention can demonstrate highreliability.

By the way, as mentioned above, the above-mentioned high-capacity modulerefers to a module handling a large electric power, including powermodules, such as an inverter, etc. Moreover, when the above-mentionedhigh-capacity module refers to a power module, the above-mentioned highexothermic element refers to a power semiconductor element, for example,and, more specifically, the above-mentioned high exothermic elementrefers to a switching element, for example.

Therefore, the ninth embodiment of the present invention is;

the high-capacity module according to any one of said fifth embodimentto said eighth embodiment of the present invention, wherein:

said high-capacity module is a power module.

Moreover, the tenth embodiment of the present invention is;

the high-capacity module according to said ninth embodiment of thepresent invention, wherein:

said high exothermic element is a switching element.

By the way, in high-capacity modules as mentioned above, for example,reduction of the noise which generates from a power semiconductorelement, such as a switching element, has been an important technicalsubject. Specifically, for example, there is a possibility thatabnormalities in switching operation of a switching element may arisedue to the noise which generates in accordance with switching operationof a switching element and may destroy a power circuit containing apower semiconductor element, such as a switching element and aperipheral circuit. Furthermore, there is also a possibility that such anoise may leak out of a high-capacity module and affect the operation ofthe peripheral equipment of the high-capacity module.

In addition, in the art, as a remedy for loss in a power semiconductorelement including, for example, IGBT, MOSFET, etc., technology trends,which use a silicon carbide (SiC) wafer or a gallium nitride (GaN) waferin place of a silicon (Si) wafer used conventionally, are becomingremarkable (for example, SiC-IGBT, SiC-MOSFET, GaN-IGBT, GaN-MOSFET,etc.). In a semiconductor element which uses such a new type of wafer,since operation in higher switching frequency is enabled as comparedwith a semiconductor element which uses a conventional Si wafer, thereis an advantage that miniaturization of a high-capacity module isenabled. However, since the frequency of a noise which generates fromthese semiconductor elements also rises with the rise of switchingfrequency, problems resulting from a noise as mentioned above alsobecome more serious. Therefore, in a high-capacity module, reduction ofa noise which generates from a power semiconductor element has been anincreasingly important technical subject.

As a countermeasure for a noise as mentioned above, it is known that itis effective to connect a capacitor (what is called a “snubbercapacitor”) in parallel with a power semiconductor. A snubber capacitorhas an effect which suppresses voltage change accompanying switchingoperation of a power semiconductor element. In order to reduce a noisemore effectively by such a snubber capacitor, it is necessary to shortenthe distance between a power semiconductor element and a snubbercapacitor. It is because the longer a wiring (wire) which electricallyconnects a power semiconductor element with a snubber capacitor becomes,the larger an equivalent inductance of the wiring becomes, and therebysurge voltage induced due to a noise which generates with switchingoperation increases, and as a result a noise reduction effect by thesnubber capacitor is not sufficiently demonstrated.

However, in a conventional high-capacity module, since it is necessaryto attach a snubber capacitor to the exterior of a high-capacity module,the wiring (wire) which electrically connects a power semiconductorelement with the snubber capacitor becomes long, and a noise reductioneffect by the snubber capacitor cannot be sufficiently demonstrated. Inaddition, in a conventional high-capacity module, a power circuitcontaining the power semiconductor element and a peripheral circuitwhich contains the control circuit element for controlling the powersemiconductor element, for example, are arranged planarly, and an areafor arranging a wiring (wire) for connecting these circuits is required.These have been factors in preventing a high-capacity module fromreduction in size and weight. Moreover, problems such as long wiringlength due to wire distribution which connects the various circuitswhich constitute a high-capacity modules as mentioned above and largeloss as a whole module, have been also recognized.

Then, it has been proposed to attempt to laminate circuit board ofvarious circuits which constitute a high-capacity module as mentionedabove to attain reduction in size and weight of the high-capacity moduleas well as improve a connection form between the various circuit boardswhich constitute the high-capacity module to attain reduction in loss ofthe high-capacity module (refer to PTL 1 to 3). In the art, for ahigh-capacity module which has such a laminated structure, aconfiguration where a snubber capacitor is mounted on a circuit board ofa peripheral circuit (drive circuit) for controlling a powersemiconductor element has been also proposed. Although such aconfiguration can shorten a wiring (wire) which electrically connectsthe power semiconductor element with the snubber capacitor, as comparedwith a configuration where a snubber capacitor is disposed in theexterior of a high-capacity module as previously mentioned, its effectis restrictive and further reduction in surge has been demanded.

Based on the backgrounds as mentioned above, the circuit board accordingto the present invention may have a capacitor embedded inside of thecircuit board in various embodiments including the above-mentionedembodiments. In accordance with such configurations, wiring whichelectrically connects a power semiconductor element with a snubbercapacitor can be further shortened as compared with a circuit boardaccording to a conventional technology. As a result, since theequivalent inductance of the wiring of the wiring decreases, surgevoltage induced due to a noise which generates with switching operationdecreases. As a result, problems that such a noise may leak out of ahigh-capacity module and affect the operation of the peripheralequipment of the high-capacity module, etc. can be further reduced.

In addition, when the capacity of a capacitor embedded inside of thecircuit board according to the present invention is increased, forexample, for the purpose of securing the capacity required for a snubbercapacitor, etc., the capacity of the capacitor can be increased byincreasing the number of laminations of the conductor (and dielectricinserted between conductors) which constitutes the capacitor. However,in this case, since the thickness of the circuit board, which has acapacitor built-in, increases, there is a possibility that it may becomean obstacle to reduction in size and weight of the high-capacity moduleusing the circuit board.

Then, in accordance with the circuit board according to the presentinvention, in the high-capacity module which has the laminationstructure as mentioned above, for the purpose of securing the capacityrequired for a snubber capacitor without increasing the thickness of thecircuit board of a peripheral circuit, an insulating layer whichcomprises the dielectric having a high dielectric constant can be formedbetween the conductors which constitute a capacitor and a capacitor canbe formed by using the insulating layer. In accordance with such aconfiguration, it becomes easy to secure the capacity required for acapacitor without increasing the number of laminations of the conductor(and dielectric inserted between conductors) which constitutes thecapacitor embedded inside of the circuit board according to the presentinvention (that is, without increasing the thickness of the circuitboard).

However, since the thermal conductivity of material which has a highdielectric constant is generally low, the thermal conductivity as thewhole circuit board, inside of which an insulating layer comprising adielectric having a high dielectric constant is formed, may decreaseand, as a result, it may become difficult to utilize the circuit boardas a heat dissipation pathway which transmits efficiently outside theheat which generates from a high exothermic element, such as a powersemiconductor element. In such a case, not by form an insulating layerwhich comprises a dielectric having a high dielectric constant so thatit may cover the whole of a plane parallel to a principal surface of acircuit board, but by partially arranging the insulating layer in aplane parallel to the principal surface of a circuit board to leave aregion where the insulating layer is not arranged in the plane, a heatconduction pathway for releasing out heat which generates from a highexothermic element through the circuit board can be secured.

Moreover, as mentioned above, in order to fully demonstrate the noisereduction effect by a snubber capacitor, it is desirable to shortenwiring which electrically connects a power semiconductor element with asnubber capacitor. Therefore, also in the circuit board according to theembodiment which has a configuration in which a capacitor is embeddedinside of a circuit board as mentioned above, it is desirable to arrangea capacitor in a position which becomes close to a high exothermicelement, such as a power semiconductor element, at the time oflamination with the first circuit board (circuit board used for thefirst electronic circuit). For example, in the second circuit board forwhich the circuit board according to the present invention is used, acapacitor can be embedded in the layer nearest to the first surface thatis a principal surface on the side which is opposed to a high exothermicelement at the time of lamination with the first circuit board.

In addition, in the layer nearest to the first surface in the secondcircuit board (circuit board used for the second electronic circuit) forwhich the circuit board according to the present invention is used,electrode(s) for attaining an electrical connection with the firstelectronic circuit containing a high exothermic element (first surfaceelectrode(s)) is disposed. Therefore, in this case, a capacitor will beembedded in the same layer as the first surface electrode(s). Thereby,in such an embodiment, since wiring which electrically connects thecapacitor embedded inside of the second circuit board with the highexothermic element can be shortened, noise reduction effect by thecapacitor can be fully demonstrated. In addition, since the conductorwhich constitutes the first surface electrode(s) is also embedded in thelayer in which the capacitor is embedded, even in a case where aninsulating layer which comprises a dielectric having a high dielectricconstant is formed between the conductors which constitute the capacitoras mentioned above, since the conductor which constitutes the firstsurface electrode(s) can be used as a heat dissipation pathway whichtransmits efficiently outside the heat which generates from the highexothermic element, such as a power semiconductor element, decrease inheat dissipation efficiency in the high-capacity module using thecircuit board as the second circuit board can be suppressed.

In accordance with these embodiments, in high-capacity modules includinga power module, such as an inverter, which are equipped with a highexothermic element, such as a power semiconductor element including aswitching element, for example, heat which generates from the highexothermic element can be transmitted outside more efficiently tofurther improve the reliability of the high-capacity module, whileattaining reduction in size and weight, reduction in surge, andreduction in a loss.

Hereafter, referring to accompanying drawings etc., configurations ofcircuit boards according to some embodiments of the present invention,etc. will be explained. However, the explanation which will be describedbelow is provided only for the purpose of exemplification, and the scopeof the present invention should not be interpreted as to be limited tothe following explanation.

Example 1. Configurations of a Circuit Board According to an Embodimentof the Present Invention and a Module Containing the Circuit Board

As mentioned above, FIG. 1 is a schematic view showing theconfigurations of a circuit board according to one embodiment of thepresent invention and a module containing the circuit board. As shown inFIG. 1, a module 100 which contains a circuit board according to oneembodiment of the present invention comprises a power circuit (firstelectronic circuit 110) containing a power semiconductor element 113(for example, IGBT etc.) and a drive circuit (second electronic circuit120) containing a circuit board 121 according to one embodiment of thepresent invention.

The first electronic circuit 110 comprises the power semiconductorelement 113 disposed through a pad for adhesion 112 on a circuit board111 of the first electronic circuit, and is disposed in a case 114formed so as to surround the side face and bottom face of the firstelectronic circuit 110, and is joined to a heat sink 115 through thebottom portion of the case 114. Therefore, heat which generates from thepower semiconductor element 113 is transmitted, through the pad foradhesion 112, the ceramic circuit board 111, and the case 114, to theheat sink 115, and is released.

On the other hand, the second electronic circuit 120 comprises variouscircuit elements such as a control circuit element 125 (for example, agate drive IC etc.) and a snubber capacitor 126 disposed on the circuitboard 121 according to the present embodiment. Second surface electrodes124 are formed as lands on the surface on the side where these circuitelements are disposed, and these circuit elements are connected throughthe lands. On the other hand, on the surface (first surface) on the sideopposite to the second surface of the circuit board 121 according to thepresent embodiment, first surface electrodes 122 for attaining anelectrical connection with the power semiconductor element 113 on thefirst electronic circuit are formed. Furthermore, at least one layer ofinner layer electrodes 123 is embedded inside of an inner layer portionof the circuit board 121 according to the present embodiment.

As mentioned above, as for the first surface electrodes 122, at least apart of conductor which constitutes the electrodes is embedded inside ofthe substrate of the circuit board 121, and at least in a region of thefirst surface, which is opposed to a terminal(s) of the powersemiconductor element 123, the conductor which constitutes the firstsurface electrodes 122 is exposed out of the substrate. Moreover, thethicknesses of the conductor which constitutes the first surfaceelectrodes 122 and the conductor which constitutes at least one layer ofthe inner layer electrodes 123 are not less than 100 micrometers.

Such second electronic circuit 120 is laminated through the powersemiconductor element 113 on the side on which the power semiconductorelement 113 of the first electronic circuit 110 is disposed, and thefirst surface electrode 122 and the terminals of the power semiconductorelement 113 are electrically connected, for example, by means ofsoldering, etc. Thereby, heat which generates from the powersemiconductor element 113 is transmitted not only through the circuitboard 111 of the first electronic circuit 110 to the heat sink 115 asmentioned above, but also through, at least, the first surface electrode122 to the ceramic circuit board 121 of the second electronic circuit120, and therefore is released more effectively.

In addition, in the present embodiment, the whole conductor, whichconstitutes the first surface electrodes 122, is embedded inside of thesubstrate and only the surface of the conductor is exposed in the sameplane as the first surface of the ceramic circuit board 111 of thesecond electronic circuit 120. Therefore, both of surfaces of thesubstrate of the ceramic circuit board 121 of the second electroniccircuit 120 and the conductor, which constitutes the first surfaceelectrodes 122, contact the power semiconductor element 113simultaneously.

Thereby, heat which generates from the power semiconductor element 113is transmitted, from the portion which directly contacts the conductorof the first surface electrodes 122 (for example, terminal part of thepower semiconductor element 113, etc.) to the conductor, and from theportion in contact with the substrate of the circuit board 121 of thesecond electronic circuit 120 to the substrate, respectively. Therefore,in the power module 100 using the circuit board 121 according to thepresent embodiment, the heat which generates from the powersemiconductor element 113 is released still more effectively, andoverheating of the module is suppressed still more effectively.

Therefore, in the power module 100 using the circuit board 121 accordingto the present embodiment, problems, such as breakage of the module bythe excessive rise in temperature resulting from the heat whichgenerates from the power semiconductor element 113 (for example,degradation of sealing resin of a circuit element which constitutes themodule, and expansion or deformation of the resin board of a peripheralcircuit) etc. are reduced.

Moreover, in the power module using the circuit board 121 according tothe present embodiment, at least a part of the conductor whichconstitutes the first surface electrodes 122 is embedded inside of thesubstrate of the circuit 121. Thereby, since the stress which acts onthe interface between the conductor and the substrate (for example,stress which generates due to the difference in the thermal expansioncoefficient between the conductor which constitutes the first surfaceelectrodes 122 and the substrate, stress which generates due to thedifference in the thermal expansion coefficient between the circuitboard 121 according to the present embodiment and the powersemiconductor element 113 and/or the circuit board 111 of the firstelectronic circuit 110, etc.) can be reduced, a highly reliablehigh-capacity module can be achieved.

Furthermore, in circuit board 121 according to the present embodiment,the conductor which constitutes the first surface electrodes 122 isexposed out of the substrate at least in the region of a first surfacewhich is the surface of the circuit board, facing the first electroniccircuit 110, and the region is opposed to a terminal(s) of the powersemiconductor element 113. Thereby, the second electronic circuit 120which contains the circuit board 121 according to the present embodimentand the power semiconductor element 113 can be connected in a shorterdistance and, for example, the surge voltage at the time of switchingcan be suppressed (reduction in surge).

Furthermore, as mentioned above, the thicknesses (in a direction whichintersects perpendicularly with the first surface) of the conductorwhich constitutes the first surface electrodes 122 and the conductorwhich constitutes at least one layer of the inner layer electrodes 123are not less than 100 micrometers. Thereby, the loss as the whole module100 including the second electronic circuit 120 that uses the circuitboard 121 according to the present embodiment can be made smaller.

As mentioned above, in accordance with the present embodiment, inhigh-capacity modules including power modules, such as an inverter,while attaining reduction in size and weight, reduction in surge, andreduction in a loss, a highly reliable circuit board for peripheralcircuits which can transmit more efficiently outside heat whichgenerates from a high exothermic element, such as a power semiconductorelement, can be provided.

2. Configuration of a High-Capacity Module According to a ConventionalTechnology

On the other hand, configuration of a power module according to aconventional technology will be explained briefly, referring to FIG. 2.As mentioned above, FIG. 2 is a schematic view showing theconfigurations of a power module according to a conventional technology.

As shown in FIG. 2, in a power module 200 according to a conventionaltechnology, on a metal base 204, a power circuit 221 containing aswitching element (IGBT 201) and a drive circuit 222 containing acontrol circuit element which controls IGBT 201 are arranged planarly,and these circuits are connected by aluminum wires 207. Therefore, inthe power module 200 according to a conventional technology, in additionto the area for arranging these circuits planarly, the area for thewiring which connects these circuits is also required, and thereforereduction size and weight of the module 200 is difficult.

Moreover, in the power module 200 according to a conventionaltechnology, since wiring length becomes longer due to the wiring of thealuminum wires 207 for connecting the power circuit 221 and the drivecircuit 222, there is a concern about problems that the loss as thewhole module 200 becomes larger, and the surge voltage which generateson switching due to the equivalent inductance of the aluminum wires 207becomes larger, etc.

On the other hand, in the circuit board according to the presentinvention and the high-capacity module using the circuit board, asmentioned above, in addition to the above-mentioned problems concernedin the power module according to a conventional technology, the problemof the heat dissipation accompanying the miniaturization of the moduleby lamination of the various circuits which constitute a high-capacitymodule can be also solved,

3. Reliability of a Circuit Board According to an Embodiment of thePresent Invention

Next, reliability of a circuit board according to an embodiment of thepresent invention will be explained below, referring to FIG. 3. Asmentioned above, FIG. 3 is a schematic view illustrating the differencein stresses acting on the interface between electrode(s) disposed at thesurface of the circuit board and the substrate of circuit boardsaccording to one embodiment of the present invention and a circuit boardaccording to a conventional technology. In FIG. 3, (a) and (b) representcircuit boards according to embodiments of the present invention, and(c) represents a circuit board according to a comparative example.

First, in the circuit board according to one embodiment of the presentinvention shown in (a), first surface electrodes 122 for attaining anelectrical connection with a high exothermic element (not shown)disposed in the first electronic circuit (not shown) is completelyembedded into the substrate of the circuit board, and only the surfacethereof is exposed in the first surface (the lower surface in FIG. 3) ofthe circuit board. Moreover, inner layer electrodes 123 are embeddedinside of the inner layer of the circuit board. Furthermore, secondsurface electrodes 124 for attaining an electrical connection withvarious circuit elements and terminals which constitute the secondelectronic circuit are embedded at the second surface side (the upperside in FIG. 3) of the circuit board, and the surface thereof is exposedout of the second surface, and constitutes lands etc.

In the circuit board according to the present embodiment, the exposedsurfaces of the first surface electrodes 122 and the first surface ofthe circuit board are in the same plane. Therefore, since a highexothermic element will also contact the substrate portion of thecircuit board as a result when the first surface electrodes 122 of thecircuit board are jointed with the high exothermic element of the firstelectronic circuit, the heat which generates from the high exothermicelement is not only released through the circuit board of the firstelectronic circuit (not shown), but also transmitted to the firstsurface electrodes and substrate of the circuit board to be releasedfrom the second surface (the upper surface in FIG. 3) of the circuitboard. Therefore, in the present embodiment, more efficient heatdissipation can be attained.

By the way, in a circuit board provided with electrode(s) like thecircuit board according to the present embodiment, as mentioned above,it is assumed that stress which generates due to the difference in athermal expansion coefficient between the conductor, which constitutethe first surface electrode(s), and the substrate, and stress whichgenerates due to the difference in a thermal expansion coefficientbetween the circuit board and a high exothermic element and/or thecircuit board of the first electronic circuit, etc. may act on theinterface between the conductor and the substrate. In this case, asshown by the circle mark in FIG. 3, the stress may concentrate on theend portion of the interface between the conductor and the substrate(corner portion of the conductor which constitutes an electrode), etc.In this case, depending on the magnitude of the stress, for example,there is a possibility that the conductor which constitutes the firstsurface electrodes may be separated from the circuit board and it maylead to the fall of the reliability of the whole module and may lead todisconnection and destruction of a circuit at worst.

However, in the circuit board according to the present embodiment, sincethe conductor which constitutes the first surface electrode(s) isembedded inside of the substrate, for example, unlike a case where aleadframe or a conductive pattern is pasted on the surface of a circuitboard, the surroundings of the portion, on which stress as mentionedabove concentrates, is covered with the substrate of the circuit board.Thereby, since the stress is relaxed and distributed, problems asmentioned above are unlikely to occur, and the reliability as the wholemodule including the electronic circuit which uses the circuit board canbe further improved.

Next, in the circuit board according to another embodiment of thepresent invention shown in (b), the first surface electrodes 122 arepartially embedded into the substrate of the circuit board and portionsother than the embedded portions are exposed at the first surface of thecircuit board. Namely, in the circuit board according to the presentembodiment, a part of the first surface electrodes partially protrudesfrom the first surface. In addition, in the circuit board according tothe present embodiment, the inner layer electrodes 123 are embeddedinside of the inner layer of the circuit board, and the second surfaceelectrodes 124 are embedded in the second surface side of the circuitboard, similarly to the embodiment of the present invention shown in theabove-mentioned (a).

In the circuit board according to the present embodiment, the exposedsurfaces of the first surface electrodes 122 (faces which are opposed tothe high exothermic element of the first electronic circuit) and thefirst surface of the circuit board are not in the same plane. Therefore,when first surface electrodes 122 of the circuit board are joined to thehigh exothermic element of the first electronic circuit, although thehigh exothermic element does not contact the substrate portion of thecircuit board, the heat which generates from the high exothermic elementis not only released through the circuit board of the first electroniccircuit (not shown), but also transmitted to the circuit board throughthe first surface electrodes, and is released from the second surface(the upper face in FIG. 3) of the circuit board.

Moreover, also in the circuit board according to the present embodiment,since the conductor which constitutes the first surface electrode(s) isembedded inside of the substrate, although being embedded partially,similarly to the embodiment of the present invention shown in theabove-mentioned (a), for example, the surroundings of the portion, onwhich stress which generates due to the difference in a thermalexpansion coefficient between the conductor, which constitute the firstsurface electrode(s), and the substrate, or stress which generates dueto the difference in a thermal expansion coefficient between the circuitboard and a high exothermic element and/or the circuit board of thefirst electronic circuit, etc. concentrates (shown by the arrow in FIG.3), is covered with the substrate of the circuit board. Thereby, sincethe stress is relaxed and distributed also in the circuit boardaccording to the present embodiment, as mentioned above, problems thatthe conductor which constitutes the first surface electrodes isseparated from the circuit board, the reliability of the whole moduledecreases, or the circuit is disconnected or destroyed are suppressed,and the reliability as the whole module including the electronic circuitwhich uses the circuit board is improved.

On the other hand, in the circuit board according to the comparativeexample shown in (c), the first surface electrodes 122 are not embeddedinside of the substrate of the circuit board, but the first surfaceelectrodes 122 are stuck on the first surface of the circuit board. Inaddition, in the circuit board according to the present comparativeexample, the inner layer electrodes 123 are embedded inside of the innerlayer of the circuit board, and the second surface electrodes 124 areembedded in the second surface side of the circuit board, similarly tothe embodiments of the present invention shown in the above-mentioned(a) and (b).

In the circuit board according to the present comparative example, asmentioned above, the first surface electrodes 122 are stuck on the firstsurface of the circuit board. Therefore, unlike the embodiments of thepresent invention shown in the above-mentioned (a) and (b), for example,the surroundings of the portion, on which stress which generates due tothe difference in a thermal expansion coefficient between the conductor,which constitute the first surface electrode(s), and the substrate,and/tress which generates due to the difference in a thermal expansioncoefficient between the circuit board and a high exothermic elementand/or the circuit board of the first electronic circuit, etc.concentrates (shown by the circle in FIG. 3), is not covered with thesubstrate of the circuit board. As a result, in the circuit boardaccording to the present comparative example, the stress is not relaxedor distributed, and there is a higher possibility that the conductorwhich constitutes the first surface electrodes may be separated from thecircuit board, the reliability of the whole module including the circuitmay decrease, and/or the circuit may be disconnected or destroyed, asmentioned above, than in the circuit board according to the presentinvention, and the reliability as the whole module including theelectronic circuit which uses the circuit board is concerned.

4. Configurations of a Circuit Board According to a Modification of thePresent Invention and a Module Containing the Circuit Board

As mentioned above, FIG. 4 is a schematic view showing theconfigurations of a circuit board according to one modification of anembodiment of the present invention, wherein a capacitor is embeddedinside of a second electronic circuit board, and a module containing thecircuit board. As shown in FIG. 4, in the high-capacity module 100according to the present modification, the snubber capacitor 126 isembedded inside of the second circuit board 121. By such aconfiguration, wiring which electrically connects the powersemiconductor element 113 and the snubber capacitor 126 can be furthershortened as compared with the circuit board according to a conventionaltechnology as mentioned above. As a result, since the equivalentinductance which the wiring has becomes smaller, the surge voltageinduced due to the noise which generates from the power semiconductorelement 113 decreases. As a result, problems that such a noise breaksthe power circuit (first electronic circuit 110) and/or the peripheralcircuit (second electronic circuit), and/or affects the operation of theperipheral equipment of the high-capacity module 100 can be furtherreduced.

In addition, in the case where the capacity of the capacitor 126embedded inside of the circuit board (the second circuit board 121)according to the present modification is increased, for example, for thepurpose of securing the capacity required for the snubber capacitor 126,etc., the capacity of the capacitor 126 can be increased by increasingthe number of laminations of the conductor (and dielectric insertedbetween the conductors) which constitutes the capacitor 126, asmentioned above. However, in this case, since the thickness of thesecond circuit board 121, which has the capacitor 126 built-in,increases, it becomes an obstacle to reduction in size and weight of thehigh-capacity module 100.

Then, in the circuit board (the second circuit board 121) according tothe present modification, in the high-capacity module 100, for thepurpose of securing the capacity required for the snubber capacitor 126without increasing the thickness of the second circuit board 121, byforming an insulating layer which comprises dielectric having a highdielectric constant between the conductors which constitute thecapacitor 126, the capacitor 126 using the insulating layer can beformed. In accordance with such a configuration, it becomes easy tosecure the capacity required for the capacitor 126 without increasingthe number of laminations of the conductor (and dielectric insertedbetween the conductors) which constitutes the capacitor 126 embeddedinside of the second circuit board 121 (that is, without increasing thethickness of the second circuit board 121).

5. Configurations of a Circuit Board According to a Modification of thePresent Invention and a Module Containing the Circuit Board

As mentioned above, FIG. 5 is a schematic view showing theconfigurations of a circuit board according to another modification ofan embodiment of the present invention, wherein a capacitor is embeddedin a part of region(s) inside of a second electronic circuit board, anda module containing the circuit board. As shown in FIG. 5, in thehigh-capacity module 100 according to the present modification, thecapacitor 126 is not formed so that it may cover the whole of a planeparallel to a principal surface of the second circuit board 121, but itis partially arranged in a plane parallel to the principal surface ofthe second circuit board 121. By such a configuration, in thehigh-capacity module 100 according to the present modification, evenwhen an insulating layer which comprises dielectric having a highdielectric constant (that is, material which has low thermalconductivity) is to be formed between the conductors which constitutethe capacitor 126 to increase the capacity of the capacitor 126 asmentioned above, a region where the insulating layer is not arranged(disposed) is left in a plane parallel to the principal surface of thesecond circuit board 121. As a result, a heat conduction pathway forreleasing out heat which generates from the high exothermic element 113through the second circuit board 121 can be secured.

6. Configurations of a Circuit Board According to a Modification of thePresent Invention and a Module Containing the Circuit Board

As mentioned above, FIG. 6 is a schematic view showing theconfigurations of a circuit board according to still anothermodification of an embodiment of the present invention, wherein acapacitor is embedded within the layer nearest to the first surfaceinside of a second electronic circuit board, and a module containing thecircuit board. As shown in FIG. 6, in the high-capacity module 100according to the present modification, the capacitor 126 is embedded inthe layer nearest to the first surface that is a principal surface onthe side which is opposed to the high exothermic element 113 at the timeof lamination with the first circuit board 111, among the dielectriclayers which constitute the second circuit board 121. By such aconfiguration, in the high-capacity module 100 according to the presentmodification, since wiring which electrically connects the capacitor 126embedded inside of the second circuit board 121 and the high exothermicelement 113 can be shortened, noise reduction effect by the capacitor126 can be fully demonstrated.

Moreover, in the second circuit board 121 according to the presentmodification, similarly to the circuit boards according to otherembodiments of the present invention, the first surface electrodes 122for attaining an electrical connection with the first electronic circuit110 containing the high exothermic element 113 is disposed on the firstsurface. Namely, in the second circuit board 121 according to thepresent modification, the capacitor 126 is embedded in the same layer asthe first surface electrodes 122. Thus, since the conductor whichconstitutes the first surface electrodes 122 is also embedded in thelayer in which the capacitor 126 is embedded, even when an insulatinglayer which comprises the dielectric having a high dielectric constantis formed between the conductors which constitute the capacitor 126 asmentioned above, the conductor which constitutes the first surfaceelectrode 122 can be used as a heat dissipation pathway which transmitsefficiently outside the heat which generates from the high exothermicelement 113, such as a power semiconductor element. As a result, also inthe high-capacity module 100 according to the present modification,decline in heat dissipation efficiency can be suppressed.

As mentioned above, the circuit board according to the present inventionis quite useful as a reliable circuit board for peripheral circuits,which can transmit more efficiently outside the heat generated fromhighly exothermic elements, such as a power semiconductor element, whileattaining reduction in size and weight, reduction in surge, andreduction in a loss, in high-capacity modules including power modules,such as an inverter. Therefore, the high-capacity module including theperipheral circuit using the circuit board according to the presentinvention can achieve high reliability by attaining higher heatdissipation efficiency, while attaining reduction in size and weight,reduction in surge, and reduction in a loss.

Although some embodiments with specific configurations have beenexplained above for the purpose of explaining the present invention, itis needless to say that the scope of the present invention is notlimited to these exemplary embodiments and various modifications can beproperly added thereto within the limits of the matter described in theclaims and specification.

REFERENCE SIGNS LIST

100: power module, 110: first electronic circuit, 111: circuit board ofthe first electronic circuit, 112: pad for adhesion, 113: powersemiconductor element, 114: case, 115: heat sink, 120: second electroniccircuit, 121: circuit board of the second electronic circuit, 122: firstsurface electrode, 123: inside layer electrode, 124: second surfaceelectrode, 125: control circuit element, 126: snubber capacitor, 200:power module, 201: IGBT, 202: diode, 203: ceramic circuit board, 204:metal base, 205: gate drive IC, 206: control circuit board, 207:aluminum wire, 209: control signal terminal, 210: power input/outputterminal, 221: power circuit, and 222: drive circuit.

The invention claimed is:
 1. A circuit board for a second electroniccircuit that is laminated on a side of a first electronic circuit onwhich a high exothermic element is disposed wherein: said circuit boardcomprises a substrate, which comprises at least one dielectric layermainly comprising ceramics, and at least one first surface electrodeformed on a first side of said circuit board that faces said firstelectronic circuit, at least a part of said first surface electrode isembedded inside of said substrate, a remaining part of said firstsurface electrode is exposed outside of said circuit board for saidsecond electronic circuit and defines a major portion of said first sideof said substrate that faces said first electronic circuit such that aportion of a first surface of said first surface electrode is opposed toat least one terminal of said high exothermic element, and the thicknessof said first surface electrode is not less than 100 micrometers in adirection perpendicular to said first surface.
 2. The circuit boardaccording to claim 1, wherein: said dielectric layer is formed of aplurality of dielectric layers and a dielectric layer forming a secondsurface which is a surface opposite to said first surface has a thermalexpansion coefficient larger than that of a dielectric layer formingsaid first surface.
 3. A circuit board for a second electronic circuitthat is laminated on a side of a first electronic circuit on which ahigh exothermic element is disposed wherein: said circuit boardcomprises a substrate, which comprises at least one dielectric layermainly comprising ceramics, at least one first surface electrode formedon a first side of said circuit board that faces said first electroniccircuit, and at least one inner layer electrode, which is embeddedinside of the dielectric layer of said circuit board, at least a part ofsaid first surface electrode is embedded inside of said substrate, aremaining part of said first surface electrode is exposed outside ofsaid circuit board for said second electronic circuit and defines amajor portion of said first side of said substrate that faces said firstelectronic circuit such that a portion of a first surface of said firstsurface electrode is opposed to at least one terminal of said highexothermic element, and the thicknesses of said first surface electrodeand said inner layer electrode are not less than 100 micrometers in adirection perpendicular to said first surface.
 4. The circuit boardaccording to claim 3, wherein: the thickness of said inner layerelectrode in a direction perpendicular to said first surface is largerthan the thickness of said first surface electrode in a directionperpendicular to said first surface.
 5. The circuit board according toclaim 4, wherein: said dielectric layer is formed of a plurality ofdielectric layers and a dielectric layer forming a second surface whichis a surface opposite to said first surface has a thermal expansioncoefficient larger than that of a dielectric layer forming said firstsurface.
 6. The circuit board according to claim 3, wherein: saiddielectric layer is formed of a plurality of dielectric layers and adielectric layer forming a second surface which is a surface opposite tosaid first surface has a thermal expansion coefficient larger than thatof a dielectric layer forming said first surface.
 7. A high-capacitymodule which comprises a first electronic circuit containing a highexothermic element, and a second electronic circuit laminated throughsaid high exothermic element on the side, on which said high exothermicelement is disposed, of said first electronic circuit, wherein: acircuit board for said second electronic circuit comprises a substrate,which comprises at least one dielectric layer mainly comprisingceramics, and at least one first surface electrode formed on a firstside of said circuit board that faces said first electronic circuit, atleast a part of said first surface electrode is embedded inside of saidsubstrate, a remaining part of said first surface electrode is exposedoutside of said circuit board for said second electronic circuit anddefines a major portion of said first side of said substrate that facessaid first electronic circuit such that a portion of a first surface ofsaid first surface electrode is opposed to at least one terminal of saidhigh exothermic element, and the thicknesses of said first surfaceelectrode is not less than 100 micrometers in a direction perpendicularto said first surface.
 8. The high-capacity module according to claim 7,wherein: said dielectric layer is formed of a plurality of dielectriclayers and a dielectric layer forming a second surface which is asurface opposite to said first surface has a thermal expansioncoefficient larger than that of a dielectric layer forming said firstsurface.
 9. A high-capacity module which comprises a first electroniccircuit containing a high exothermic element, and a second electroniccircuit laminated through said high exothermic element on the side, onwhich said high exothermic element is disposed, of said first electroniccircuit, wherein: a circuit board for said second electronic circuitcomprises a substrate, which comprises at least one dielectric layermainly comprising ceramics, and at least one first surface electrodeformed on a first side of said circuit board that faces said firstelectronic circuit, and at least one inner layer electrode which isembedded inside of inner layer(s) of said circuit board, at least a partof said first surface electrode is embedded inside of said substrate, aremaining part of said first surface electrode is exposed outside ofsaid circuit board for said second electronic circuit and defines amajor portion of said first side of said substrate that faces said firstelectronic circuit such that a portion of a first surface of said firstsurface electrode is opposed to at least one terminal of said highexothermic element, and the thicknesses of said first surface electrodeand said inner layer electrode is not less than 100 micrometers in adirection perpendicular to said first surface.
 10. The high-capacitymodule according to claim 9, wherein: the thickness of said inner layerelectrode in a direction perpendicular to said first surface is largerthan the thickness of said first surface electrode in a directionperpendicular to said first surface.
 11. The high-capacity moduleaccording to claim 10, wherein: said dielectric layer is formed of aplurality of dielectric layers and a dielectric layer forming a secondsurface which is a surface opposite to said first surface has a thermalexpansion coefficient larger than that of a dielectric layer formingsaid first surface.
 12. The high-capacity module according to claim 9,wherein: said dielectric layer is formed of a plurality of dielectriclayers and a dielectric layer forming a second surface which is asurface opposite to said first surface has a thermal expansioncoefficient larger than that of a dielectric layer forming said firstsurface.